1. Field of the Invention
The present invention relates to a method for manufacturing a capsule toner.
2. Description of the Related Art
As a method for manufacturing a toner, a wide variety of kneading pulverization methods have been conventionally used, but since the pulverized toner usually has an irregular shape with a lot of unevenness on the surface thereof and the broken surface after pulverization becomes the surface of the toner particle as it is, the surface composition thereof easily becomes non-uniform and it is hard to uniformly regulate the surface state of the toner particle. If the shape of the toner particle surface has an irregular shape with a lot of unevenness, there are problems, for example, in that flowability of the toner is reduced or non-uniformity of the toner composition is caused, and further, fogging or toner spatter, and the like occur.
In consideration of such problems of the irregular shape of the toner particle surface, various wet methods in which a dispersion liquid of toner raw materials is mixed and aggregated to manufacture a toner have been suggested, which may replace the kneading pulverization method. However, in the case of the wet methods, there are drawbacks that since dispersion stabilizing agents or aggregating agents are widely used, a part of the components remain on the toner particle surface or the inside thereof, thereby causing reduction in moisture resistance or deterioration of charge characteristics, and in particular, creation of instability of charge characteristics.
Meanwhile, as there has been a recent demand for high-quality images, there has been a tendency that the particle size of toners has progressively become smaller and the content of a toner having a small particle size as fine powders in the two-component developer has increased. In a two-component developer including a toner having a small particle size, there occurs toner spent into a carrier owing to cracks of a toner having a small particle size due to the stress inside a developing device or change in the shape, and correspondingly, deterioration of the charge of the developer, and further, a development or transfer process is caused to be affected, thereby leading to deterioration of image quality.
Furthermore, as images have recently become colored, there is a tendency that the color toner is progressively subjected to low-temperature fixing and low-temperature softening materials are used as toner components.
Accordingly, as a toner having good flowability, transfer property, or the like, uniform charge performance, an excellent anti-offset property, and other various functions, a capsule toner in which the surface of a toner base particle is coated with a resin layer is proposed.
Japanese Unexamined Patent Publication JP-A 63-198070 (1988) discloses an electrostatic toner in which toner particles, hydrophobic fine resin particles, and other required fine particles are mixed by means of mechanical strain, and the surfaces of the toner particles are coated.
As a method for preparing a capsule toner, a method of spraying a liquid for plasticizing toner base particles and fine resin particles to form a coating layer is known, and this method is advantageous in that the resin coating layer is uniformly formed.
However, according to the conditions for spraying the liquid, the spray liquid cannot be uniformly sprayed on a mixture of the toner base particles and the fine resin particles, and as a result, there occur aggregation of the mixture occurs or adherence thereof to the inner wall of the apparatus, and reduction in a yield as well as non-uniformity in thickness of the coating layer.
Furthermore, a toner having non-uniform thickness of the coating layer easily varies in the image densities and has poor fixability, and also, a developer including the toner causes a problem in terms of high-temperature stability.